1. Field of the Invention
The present invention relates to a fastening element for mineral constructional components and including a shaft having rotatable application means, a tapping thread extending, at least regionwise, along the shaft, and a coating provided on the shaft, at least regionwise.
2. Description of the Prior Art
German Publication DE 102 43 537 A1 discloses a fastening element for mineral constructional components and having a shaft. At one end of the shaft, there is provided, e.g., a hexagonal head as a rotatable application means, for a setting tool, and a tapping thread that extends, starting from the shaft end opposite the rotatable application means, along the shaft at least regionwise. The shaft is provided, regionwise, with a coating of eleastomeric material. The strength of the coating is so selected that upon screwing of the fastening element in, it becomes partially compressed sealing the intermediate space between the core of the fastening element and the borehole wall. This fastening element can be unscrewed, without parts of the provided coating remaining in the constructional component.
The drawback of the proposes solution consists in that for setting a fastening element with an elastomeric coating high screw-in torques are necessary which exceed power limits of a number of screw-driving power tools or even the torsional strength of a fastening element. Because the preliminary formed borehole has a round cross-section only in theory, sealing of the borehole is not ensured at each application. The connection between the elastoemeric coating and the core of the fastening element can be broken by loss of adhesion to the threaded surface. As a result, not at each application, a high bearing capacity is ensured by the coating. Further, the deformation of the elastomeric coating leads to generation of expanding forces in the gap which can lead, in particular in the region of the borehole mouth and at small edge and axial distances of the fastening elements, to spalling on the surface of the constructional component.
Accordingly, an object of the present invention is to provide a thread-tapping fastening element that can be easily set and loaded immediately after setting.
Another object of the present invention is to provide a thread-tapping fastening element that has an increased bearing capacity in comparison with conventional thread-tapping fastening elements and can be easily unscrewed.